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Merge pull request #65 from ehudt/master

Adds a CYK parser to lark.
tags/gm/2021-09-23T00Z/github.com--lark-parser-lark/0.5.3
Erez Shinan 6 years ago
committed by GitHub
parent
commit
20a8de93c8
No known key found for this signature in database GPG Key ID: 4AEE18F83AFDEB23
7 changed files with 441 additions and 8 deletions
  1. +6
    -2
      lark/lark.py
  2. +59
    -2
      lark/parser_frontends.py
  3. +361
    -0
      lark/parsers/cyk.py
  4. +1
    -2
      lark/parsers/earley.py
  5. +2
    -1
      lark/tree.py
  6. +1
    -0
      tests/__main__.py
  7. +11
    -1
      tests/test_parser.py

+ 6
- 2
lark/lark.py View File

@@ -59,7 +59,7 @@ class LarkOptions(object):
self.propagate_positions = o.pop('propagate_positions', False)
self.earley__predict_all = o.pop('earley__predict_all', False)

assert self.parser in ('earley', 'lalr', None)
assert self.parser in ('earley', 'lalr', 'cyk', None)

if self.parser == 'earley' and self.transformer:
raise ValueError('Cannot specify an embedded transformer when using the Earley algorithm.'
@@ -131,6 +131,8 @@ class Lark:
self.options.lexer = 'standard'
elif self.options.parser == 'earley':
self.options.lexer = 'dynamic'
elif self.options.parser == 'cyk':
self.options.lexer = 'standard'
else:
assert False, self.options.parser
lexer = self.options.lexer
@@ -140,7 +142,9 @@ class Lark:
if self.options.parser == 'earley':
self.options.ambiguity = 'resolve'
else:
assert self.options.parser == 'earley', "Only Earley supports disambiguation right now"
disambig_parsers = ['earley', 'cyk']
assert self.options.parser in disambig_parsers, (
'Only %s supports disambiguation right now') % ', '.join(disambig_parsers)
assert self.options.ambiguity in ('resolve', 'explicit', 'auto', 'resolve__antiscore_sum')

# Parse the grammar file and compose the grammars (TODO)


+ 59
- 2
lark/parser_frontends.py View File

@@ -1,10 +1,13 @@
import re
from .utils import get_regexp_width

from .parsers.grammar_analysis import GrammarAnalyzer
from .lexer import Lexer, ContextualLexer, Token

from .common import is_terminal, GrammarError, ParserConf
from .parsers import lalr_parser, earley, xearley, resolve_ambig
from .common import GrammarError
from .common import is_terminal, GrammarError
from .parsers import lalr_parser, earley, xearley, resolve_ambig, cyk
from .tree import Tree

class WithLexer:
def init_traditional_lexer(self, lexer_conf):
@@ -134,6 +137,55 @@ class XEarley:
def parse(self, text):
return self.parser.parse(text)


class Earley(WithLexer):
def __init__(self, lexer_conf, parser_conf, options=None):
self.init_traditional_lexer(lexer_conf)

self.parser = earley.Parser(parser_conf, self.match,
resolve_ambiguity=get_ambiguity_resolver(options))

def match(self, term, token):
return term == token.type

def parse(self, text):
tokens = self.lex(text)
return self.parser.parse(tokens)

class CYK(WithLexer):

def __init__(self, lexer_conf, parser_conf, options=None):
self.init_traditional_lexer(lexer_conf)

self._analysis = GrammarAnalyzer(parser_conf)
self._parser = cyk.Parser(self._analysis.rules, parser_conf.start)

self._postprocess = {}
for rule in self._analysis.rules:
a = rule.alias
self._postprocess[a] = a if callable(a) else (a and getattr(parser_conf.callback, a))

def parse(self, text):
tokens = list(self.lex(text))
parse = self._parser.parse(tokens)
parse = self._transform(parse)
return parse

def _transform(self, tree):
subtrees = list(tree.iter_subtrees())
for subtree in subtrees:
subtree.children = [self._apply_callback(c) if isinstance(c, Tree) else c for c in subtree.children]

return self._apply_callback(tree)

def _apply_callback(self, tree):
children = tree.children
callback = self._postprocess[tree.rule.alias]
assert callback, tree.rule.alias
r = callback(children)
return r


def get_frontend(parser, lexer):
if parser=='lalr':
if lexer is None:
@@ -155,6 +207,11 @@ def get_frontend(parser, lexer):
raise ValueError('The Earley parser does not support the contextual parser')
else:
raise ValueError('Unknown lexer: %s' % lexer)
elif parser == 'cyk':
if lexer == 'standard':
return CYK
else:
raise ValueError('CYK parser requires using standard parser.')
else:
raise ValueError('Unknown parser: %s' % parser)



+ 361
- 0
lark/parsers/cyk.py View File

@@ -0,0 +1,361 @@
"""This module implements a CYK parser."""

from collections import defaultdict
import itertools

from ..common import ParseError, is_terminal
from ..lexer import Token
from ..tree import Tree

try:
xrange
except NameError:
xrange = range

class Symbol(object):
"""Any grammar symbol."""

def __init__(self, s):
self.s = s

def __repr__(self):
return '%s(%s)' % (type(self).__name__, str(self))

def __str__(self):
return str(self.s)

def __eq__(self, other):
return self.s == str(other)

def __ne__(self, other):
return not self.__eq__(other)

def __hash__(self):
return hash((type(self), str(self.s)))


class T(Symbol):
"""Terminal."""

def match(self, s):
return self.s == s.type


class NT(Symbol):
"""Non-terminal."""
pass


class Rule(object):
"""Context-free grammar rule."""

def __init__(self, lhs, rhs, weight, alias):
super(Rule, self).__init__()
assert isinstance(lhs, NT), lhs
assert all(isinstance(x, NT) or isinstance(x, T) for x in rhs), rhs
self.lhs = lhs
self.rhs = rhs
self.weight = weight
self.alias = alias

def __str__(self):
return '%s -> %s' % (str(self.lhs), ' '.join(str(x) for x in self.rhs))

def __repr__(self):
return str(self)

def __hash__(self):
return hash((self.lhs, tuple(self.rhs)))

def __eq__(self, other):
return self.lhs == other.lhs and self.rhs == other.rhs

def __ne__(self, other):
return not (self == other)


class Grammar(object):
"""Context-free grammar."""

def __init__(self, rules):
self.rules = frozenset(rules)

def __eq__(self, other):
return self.rules == other.rules

def __str__(self):
return '\n' + '\n'.join(sorted(repr(x) for x in self.rules)) + '\n'

def __repr__(self):
return str(self)


# Parse tree data structures
class RuleNode(object):
"""A node in the parse tree, which also contains the full rhs rule."""

def __init__(self, rule, children, weight=0):
self.rule = rule
self.children = children
self.weight = weight

def __repr__(self):
return 'RuleNode(%s, [%s])' % (repr(self.rule.lhs), ', '.join(str(x) for x in self.children))



class Parser(object):
"""Parser wrapper."""

def __init__(self, rules, start):
super(Parser, self).__init__()
self.orig_rules = {rule.alias: rule for rule in rules}
rules = [self._to_rule(rule) for rule in rules]
self.grammar = to_cnf(Grammar(rules))
self.start = NT(start)

def _to_rule(self, lark_rule):
"""Converts a lark rule, (lhs, rhs, callback, options), to a Rule."""
return Rule(
NT(lark_rule.origin), [
T(x) if is_terminal(x) else NT(x) for x in lark_rule.expansion
], weight=lark_rule.options.priority if lark_rule.options and lark_rule.options.priority else 0, alias=lark_rule.alias)

def parse(self, tokenized): # pylint: disable=invalid-name
"""Parses input, which is a list of tokens."""
table, trees = _parse(tokenized, self.grammar)
# Check if the parse succeeded.
if all(r.lhs != self.start for r in table[(0, len(tokenized) - 1)]):
raise ParseError('Parsing failed.')
parse = trees[(0, len(tokenized) - 1)][NT(self.start)]
return self._to_tree(revert_cnf(parse))

def _to_tree(self, rule_node):
"""Converts a RuleNode parse tree to a lark Tree."""
orig_rule = self.orig_rules[rule_node.rule.alias]
children = []
for i, child in enumerate(rule_node.children):
if isinstance(child, RuleNode):
children.append(self._to_tree(child))
else:
assert isinstance(child.s, Token)
children.append(child.s)
return Tree(orig_rule.origin, children, rule=orig_rule)


def print_parse(node, indent=0):
if isinstance(node, RuleNode):
print(' ' * (indent * 2) + str(node.rule.lhs))
for child in node.children:
print_parse(child, indent + 1)
else:
print(' ' * (indent * 2) + str(node.s))


def _parse(s, g):
"""Parses sentence 's' using CNF grammar 'g'."""
# The CYK table. Indexed with a 2-tuple: (start pos, end pos)
table = defaultdict(set)
# Top-level structure is similar to the CYK table. Each cell is a dict from
# rule name to the best (lightest) tree for that rule.
trees = defaultdict(dict)
# Populate base case with existing terminal production rules
for i, w in enumerate(s):
for terminal, rules in g.terminal_rules.items():
if terminal.match(w):
for rule in rules:
table[(i, i)].add(rule)
if (rule.lhs not in trees[(i, i)] or
rule.weight < trees[(i, i)][rule.lhs].weight):
trees[(i, i)][rule.lhs] = RuleNode(rule, [T(w)], weight=rule.weight)

# Iterate over lengths of sub-sentences
for l in xrange(2, len(s) + 1):
# Iterate over sub-sentences with the given length
for i in xrange(len(s) - l + 1):
# Choose partition of the sub-sentence in [1, l)
for p in xrange(i + 1, i + l):
span1 = (i, p - 1)
span2 = (p, i + l - 1)
for r1, r2 in itertools.product(table[span1], table[span2]):
for rule in g.nonterminal_rules.get((r1.lhs, r2.lhs), []):
table[(i, i + l - 1)].add(rule)
r1_tree = trees[span1][r1.lhs]
r2_tree = trees[span2][r2.lhs]
rule_total_weight = rule.weight + r1_tree.weight + r2_tree.weight
if (rule.lhs not in trees[(i, i + l - 1)]
or rule_total_weight < trees[(i, i + l - 1)][rule.lhs].weight):
trees[(i, i + l - 1)][rule.lhs] = RuleNode(rule, [r1_tree, r2_tree], weight=rule_total_weight)
return table, trees


# This section implements context-free grammar converter to Chomsky normal form.
# It also implements a conversion of parse trees from its CNF to the original
# grammar.
# Overview:
# Applies the following operations in this order:
# * TERM: Eliminates non-solitary terminals from all rules
# * BIN: Eliminates rules with more than 2 symbols on their right-hand-side.
# * UNIT: Eliminates non-terminal unit rules
#
# The following grammar characteristics aren't featured:
# * Start symbol appears on RHS
# * Empty rules (epsilon rules)


class CnfWrapper(object):
"""CNF wrapper for grammar.

Validates that the input grammar is CNF and provides helper data structures.
"""

def __init__(self, grammar):
super(CnfWrapper, self).__init__()
self.grammar = grammar
self.rules = grammar.rules
self.terminal_rules = defaultdict(list)
self.nonterminal_rules = defaultdict(list)
for r in self.rules:
# Validate that the grammar is CNF and populate auxiliary data structures.
assert isinstance(r.lhs, NT), r
assert len(r.rhs) in [1, 2], r
if len(r.rhs) == 1 and isinstance(r.rhs[0], T):
self.terminal_rules[r.rhs[0]].append(r)
elif len(r.rhs) == 2 and all(isinstance(x, NT) for x in r.rhs):
self.nonterminal_rules[tuple(r.rhs)].append(r)
else:
assert False, r

def __eq__(self, other):
return self.grammar == other.grammar

def __repr__(self):
return repr(self.grammar)


class UnitSkipRule(Rule):
"""A rule that records NTs that were skipped during transformation."""

def __init__(self, lhs, rhs, skipped_rules, weight, alias):
super(UnitSkipRule, self).__init__(lhs, rhs, weight, alias)
self.skipped_rules = skipped_rules

def __eq__(self, other):
return isinstance(other, type(self)) and self.skipped_rules == other.skipped_rules

__hash__ = Rule.__hash__


def build_unit_skiprule(unit_rule, target_rule):
skipped_rules = []
if isinstance(unit_rule, UnitSkipRule):
skipped_rules += unit_rule.skipped_rules
skipped_rules.append(target_rule)
if isinstance(target_rule, UnitSkipRule):
skipped_rules += target_rule.skipped_rules
return UnitSkipRule(unit_rule.lhs, target_rule.rhs, skipped_rules,
weight=unit_rule.weight + target_rule.weight, alias=unit_rule.alias)


def get_any_nt_unit_rule(g):
"""Returns a non-terminal unit rule from 'g', or None if there is none."""
for rule in g.rules:
if len(rule.rhs) == 1 and isinstance(rule.rhs[0], NT):
return rule
return None


def _remove_unit_rule(g, rule):
"""Removes 'rule' from 'g' without changing the langugage produced by 'g'."""
new_rules = [x for x in g.rules if x != rule]
refs = [x for x in g.rules if x.lhs == rule.rhs[0]]
new_rules += [build_unit_skiprule(rule, ref) for ref in refs]
return Grammar(new_rules)


def _split(rule):
"""Splits a rule whose len(rhs) > 2 into shorter rules."""
rule_str = str(rule.lhs) + '__' + '_'.join(str(x) for x in rule.rhs)
rule_name = '__SP_%s' % (rule_str) + '_%d'
yield Rule(rule.lhs, [rule.rhs[0], NT(rule_name % 1)], weight=rule.weight, alias=rule.alias)
for i in xrange(1, len(rule.rhs) - 2):
yield Rule(NT(rule_name % i), [rule.rhs[i], NT(rule_name % (i + 1))], weight=0, alias='Split')
yield Rule(NT(rule_name % (len(rule.rhs) - 2)), rule.rhs[-2:], weight=0, alias='Split')


def _term(g):
"""Applies the TERM rule on 'g' (see top comment)."""
all_t = {x for rule in g.rules for x in rule.rhs if isinstance(x, T)}
t_rules = {t: Rule(NT('__T_%s' % str(t)), [t], weight=0, alias='Term') for t in all_t}
new_rules = []
for rule in g.rules:
if len(rule.rhs) > 1 and any(isinstance(x, T) for x in rule.rhs):
new_rhs = [t_rules[x].lhs if isinstance(x, T) else x for x in rule.rhs]
new_rules.append(Rule(rule.lhs, new_rhs, weight=rule.weight, alias=rule.alias))
new_rules.extend(v for k, v in t_rules.items() if k in rule.rhs)
else:
new_rules.append(rule)
return Grammar(new_rules)


def _bin(g):
"""Applies the BIN rule to 'g' (see top comment)."""
new_rules = []
for rule in g.rules:
if len(rule.rhs) > 2:
new_rules += _split(rule)
else:
new_rules.append(rule)
return Grammar(new_rules)


def _unit(g):
"""Applies the UNIT rule to 'g' (see top comment)."""
nt_unit_rule = get_any_nt_unit_rule(g)
while nt_unit_rule:
g = _remove_unit_rule(g, nt_unit_rule)
nt_unit_rule = get_any_nt_unit_rule(g)
return g


def to_cnf(g):
"""Creates a CNF grammar from a general context-free grammar 'g'."""
g = _unit(_bin(_term(g)))
return CnfWrapper(g)


def unroll_unit_skiprule(lhs, orig_rhs, skipped_rules, children, weight, alias):
if not skipped_rules:
return RuleNode(Rule(lhs, orig_rhs, weight=weight, alias=alias), children, weight=weight)
else:
weight = weight - skipped_rules[0].weight
return RuleNode(
Rule(lhs, [skipped_rules[0].lhs], weight=weight, alias=alias), [
unroll_unit_skiprule(skipped_rules[0].lhs, orig_rhs,
skipped_rules[1:], children,
skipped_rules[0].weight, skipped_rules[0].alias)
], weight=weight)


def revert_cnf(node):
"""Reverts a parse tree (RuleNode) to its original non-CNF form (Node)."""
if isinstance(node, T):
return node
# Reverts TERM rule.
if node.rule.lhs.s.startswith('__T_'):
return node.children[0]
else:
children = []
for child in map(revert_cnf, node.children):
# Reverts BIN rule.
if isinstance(child, RuleNode) and child.rule.lhs.s.startswith('__SP_'):
children += child.children
else:
children.append(child)
# Reverts UNIT rule.
if isinstance(node.rule, UnitSkipRule):
return unroll_unit_skiprule(node.rule.lhs, node.rule.rhs,
node.rule.skipped_rules, children,
node.rule.weight, node.rule.alias)
else:
return RuleNode(node.rule, children)

+ 1
- 2
lark/parsers/earley.py View File

@@ -22,8 +22,7 @@ class Derivation(Tree):
_hash = None

def __init__(self, rule, items=None):
Tree.__init__(self, 'drv', items or [])
self.rule = rule
Tree.__init__(self, 'drv', items or [], rule=rule)

def _pretty_label(self): # Nicer pretty for debugging the parser
return self.rule.origin if self.rule else self.data


+ 2
- 1
lark/tree.py View File

@@ -9,9 +9,10 @@ from .utils import inline_args

###{standalone
class Tree(object):
def __init__(self, data, children):
def __init__(self, data, children, rule=None):
self.data = data
self.children = list(children)
self.rule = rule

def __repr__(self):
return 'Tree(%s, %s)' % (self.data, self.children)


+ 1
- 0
tests/__main__.py View File

@@ -16,6 +16,7 @@ except ImportError:
from .test_parser import (
TestLalrStandard,
TestEarleyStandard,
TestCykStandard,
TestLalrContextual,
TestEarleyScanless,
TestEarleyDynamic,


+ 11
- 1
tests/test_parser.py View File

@@ -382,6 +382,7 @@ def _make_parser_test(LEXER, PARSER):
g.parse(u'\xa3\u0101\u00a3\u0203\n')


@unittest.skipIf(PARSER == 'cyk', "Takes forever")
def test_stack_for_ebnf(self):
"""Verify that stack depth isn't an issue for EBNF grammars"""
g = _Lark(r"""start: a+
@@ -455,6 +456,7 @@ def _make_parser_test(LEXER, PARSER):



@unittest.skipIf(PARSER == 'cyk', "No empty rules")
def test_empty_expand1_list(self):
g = _Lark(r"""start: list
?list: item*
@@ -473,6 +475,7 @@ def _make_parser_test(LEXER, PARSER):
[list] = r.children
self.assertSequenceEqual([item.data for item in list.children], ())

@unittest.skipIf(PARSER == 'cyk', "No empty rules")
def test_empty_expand1_list_2(self):
g = _Lark(r"""start: list
?list: item* "!"?
@@ -492,6 +495,7 @@ def _make_parser_test(LEXER, PARSER):
self.assertSequenceEqual([item.data for item in list.children], ())


@unittest.skipIf(PARSER == 'cyk', "No empty rules")
def test_empty_flatten_list(self):
g = _Lark(r"""start: list
list: | item "," list
@@ -645,6 +649,7 @@ def _make_parser_test(LEXER, PARSER):
self.assertEqual(len(x.children), 1, '/a/ should not be considered anonymous')
self.assertEqual(x.children[0].type, "A")

@unittest.skipIf(PARSER == 'cyk', "No empty rules")
def test_maybe(self):
g = _Lark("""start: ["a"] """)
x = g.parse('a')
@@ -702,6 +707,7 @@ def _make_parser_test(LEXER, PARSER):
# B: A
# """)

@unittest.skipIf(PARSER == 'cyk', "No empty rules")
def test_empty(self):
# Fails an Earley implementation without special handling for empty rules,
# or re-processing of already completed rules.
@@ -732,6 +738,8 @@ def _make_parser_test(LEXER, PARSER):

def test_float_without_lexer(self):
expected_error = UnexpectedInput if LEXER == 'dynamic' else UnexpectedToken
if PARSER == 'cyk':
expected_error = ParseError

g = _Lark("""start: ["+"|"-"] float
float: digit* "." digit+ exp?
@@ -796,6 +804,7 @@ def _make_parser_test(LEXER, PARSER):
self.assertEqual(tree.children, ['a', 'A'])


@unittest.skipIf(PARSER == 'cyk', "No empty rules")
def test_twice_empty(self):
g = """!start: [["A"]]
"""
@@ -1001,6 +1010,7 @@ def _make_parser_test(LEXER, PARSER):


@unittest.skipIf(LEXER==None, "Scanless doesn't support regular expressions")
@unittest.skipIf(PARSER == 'cyk', "No empty rules")
def test_ignore(self):
grammar = r"""
COMMENT: /(!|(\/\/))[^\n]*/
@@ -1026,7 +1036,6 @@ def _make_parser_test(LEXER, PARSER):
self.assertEqual(tree.children, [])



@unittest.skipIf(LEXER==None, "Scanless doesn't support regular expressions")
def test_regex_escaping(self):
g = _Lark("start: /[ab]/")
@@ -1075,6 +1084,7 @@ def _make_parser_test(LEXER, PARSER):
# Note: You still have to import them in __main__ for the tests to run
_TO_TEST = [
('standard', 'earley'),
('standard', 'cyk'),
('dynamic', 'earley'),
('standard', 'lalr'),
('contextual', 'lalr'),


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